Automotive instrument panels and door panels are typically composites which are made of a rigid backing which supports a semi-rigid urethane foam with the semi-rigid urethane foam being covered with a skin compound. Such skin compounds are typically blends of polyvinyl chloride (PVC) with a nitrile rubber (NBR). The nitrile rubber is included in such blends as a permanent modifier for the PVC which provides it with a higher degree of flexibility.
The automotive industry is currently moving toward more aerodynamic body designs. These new aerodynamic designs typically include larger glass surface areas. Such design changes have significantly increased the heat and ultraviolet light aging requirements of automotive interiors. This has, in turn, significantly increased the demands put upon polymers utilized as skins in automotive interior panels.
Heat and light stabilizers can be employed to improve the heat and ultraviolet light aging characteristics of conventional PVC/NBR blends which are utilized as skins for automotive interior panels. However, the degree to which the aging characteristics of such blends can be improved by the addition of additives is limited. In fact, there is a demand for performance characteristics in such applications which cannot be realized by the utilization of heat and light stabilizers alone. For instance, it would be highly desirable for the skins used in automotive panels to resist discoloration and cracking under conditions of high heat and intense ultraviolet light throughout the life of the vehicle.
NBR/PVC blends offer an array of physical properties making them useful as a skin composition for automotive panels. The NBR acts as a permanent flexibilizing monomer for the PVC. It also acts as a shrinkage control agent, and embossing aid, and improves grain retention. The NBR in such blends further provides vacuum-forming gauge control and exhibits low fog characteristics. NSPR is highly compatible with PVC and has the capability of being recycled. It is essential for any polymer that is substituted for NBR to display these essential characteristics.
U.S. Pat. No. 5,380,785 discloses rubbery polymer which can be blended with polyvinyl chloride to make leathery compositions having good heat and ultraviolet light resistance, said rubbery polymer being comprised of repeat units which are derived from (a) butyl acrylate, or optionally a mixture of butyl acrylate and 2-ethylhexyl acrylate containing up to about 40 percent 2-ethylhexyl acrylate, (b) at least one member selected from the group consisting of methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate, (c) acrylonitrile, (d) styrene, (e) a half ester maleate soap and (f) a crosslinking agent. However, it would be highly desirable to increase the color stability of such rubbery polymers.